081 FXUS63 KIND 270838 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 338 AM EST Sun Dec 27 2020 .UPDATE... The SYNOPSIS...NEAR TERM...SHORT TERM and LONG TERM Sections have been updated below. && .SYNOPSIS... Issued at 333 AM EST Sun Dec 27 2020 Dry and seasonably warm conditions today with winds occasionally gusting upwards of 30 mph. A quick moving system will pass through during the early overnight hours with a quick tenth of an inch of rain expected for much of central Indiana. Dry weather then briefly returns Monday and Tuesday before a much stronger system brings widespread rain Wednesday into Thursday followed by accumulating snow Thursday night and Friday. Snow amounts remain quite uncertain with higher confidence in the widespread rain. && .NEAR TERM /Today/... Issued at 333 AM EST Sun Dec 27 2020 Strong surface southerly flow will advect warm, moist air into central Indiana through the day today as a surface low pressure tracks across the Central Plains. Indiana will remain smashed between this low pressure and a broad area of high pressure across the Eastern United States. As the low nears, pressure gradients will increase along with a strengthening LLJ at 850mb. By late today, winds at 5000ft will be nearly 60kts, but conditions do not look favorable for mixing down of these winds with a strong inversion just off the surface. With that in mind, do think there will be frequent gusts up to 30 mph, but gusts above that will be infrequent and isolated. This strong southerly warm air advection should be enough to counteract the increasing clouds by mid afternoon, so increased highs above model guidance with temps ranging from the mid 40s in the north to the low 50s in the south. && .SHORT TERM /Tonight through Tuesday night/... Issued at 333 AM EST Sun Dec 27 2020 The aforementioned low pressure system will be moving from the Central Plains into the Upper Midwest during the overnight hours tonight with a surface cold front nearing the area at the start of the period. Current expectations are that the cold front passes through shortly after midnight with light rain out ahead of the front and then briefly after the passage. Even with the ample southerly flow today, the fast motion of the system will keep QPF amounts fairly minimal with around a tenth of an inch of rain expected with highest amounts across the northern counties where the forcing will be to be strongest. High pressure will then quickly build in the aftermath of the frontal passage with colder air moving in as flow switches from the south to the northwest. Quiet and seasonable weather is then expected Monday and Tuesday with the high pressure and upper level ridging in place. The pattern will begin to shift Tuesday night as a much stronger low pressure system builds in the lee of the Rockies and begins to track to the northeast. During the overnight hours on Tuesday, flow will again shift to be more southerly with a very similar pattern to the weather that is expected today with high pressure in the east and a surface low tracking across the Plains. There may be a brief period of precipitation across the northwestern counties late Tuesday night as the system nears, but confidence remains low. Confidence in precipitation type is even lower with a combination of rain, snow, and freezing rain possible. Highs will climb into the low to mid 30s on Monday and Tuesday. Lows will fall into the upper 20s and low 30s tonight and Tuesday night. Lows will dip into the upper teens to low 20s on Monday night. && .LONG TERM /Wednesday through Saturday/... Issued at 333 AM EST Sun Dec 27 2020 Complex systems may make quite a splash rounding out the old year and bring in the new one. Models in slightly closer in agreement in timing at the onset. Northern stream wave will start off the more active one. This system will dart off to the eastern great lakes and Quebec on Thursday. Associated warm front will lift north across central Indiana Wednesday as a 60 knot low level jet moves overhead. That combined with deep moisture, an approaching cold front and a 150 plus low level jet over the upper Midwest (central Indiana in favorable right rear quadrant) supports increasing chances of rain Wednesday. The cold front will move through Wednesday night with models hinting around that a wave or two may develop along the front in response to deepening Texas upper low. This would suggest widespread rain Wednesday per the blend. Could see the rain briefly mix with snow over northwestern sections early Thursday, otherwise, thermals support rain and models having some differences whether or not the activity will briefly end from northwest to southeast Thursday afternoon behind the front. Strong warm advection supports the well above normal temperatures in the 50s on Wednesday despite increased cloud cover and rain. Could see over an inch of rain through Thursday. This could cause some minor water issues. More precipitation will return Thursday night and Friday as the southern upper low ejects northeast over the Ohio Valley/Great Lakes. Models having issues with the track of that feature with the 00z GFS much further south than the 00z ECMWF. The 00z Canadian was a compromise and took the upper low across the heart of central Indiana late Friday. The actual track of this system will determine precipitation type and where the highest amounts of any snow will be. For now, with confidence in the eventual correct track lacking, too soon for any pseudo snowfall accumulation forecast. All models quickly move the second system well northeast and move high pressure to the Ohio Valley Friday night and Saturday. This will allow for dry and seasonable remainder to next weekend. && .AVIATION (Discussion for the 270600Z TAF Issuance)... Issued at 1131 PM EST Sat Dec 26 2020 IMPACTS: VFR through about 23Z...then MVFR conditions Gusty winds develop Sunday afternoon LLWS also develops Sunday afternoon Rain is possible Sunday evening DISCUSSION: A low level jet will develop ahead of an approaching cold front Sunday afternoon, providing wind gusts over 20kt along with LLWS. MVFR conditions and some rain will accompany the front. CONFIDENCE: High confidence in VFR through much of the day Sun. High confidence in winds and LLWS. && .IND WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...White NEAR TERM...White SHORT TERM...White LONG TERM....Koch AVIATION...50